If you're renting a car, chances are pretty good that you can make it. In '06 and '07 we landed around 10:30. DH went downstairs to the Dollar counter and got the rental car while the kids and I waited for the luggage. By the time the bags were there, he was done with the car paperwork and we headed right out. In '06 we checked into POR at 11:30 and in '07 we checked into Pop....both times, the rooms were ready.

You could always go to DTD or play a round of mini golf if you don't want to go to a park that day. Once you have your KTTW cards, you can use your resort pool. The POR food court is really great (my kids always ask to go there, even when we aren't staying at POR), so you may want to have a counter service lunch. The boat to DTD is fun, too.

I think the chances are about the same as checking in "early" at any resort or hotel. It depends on when the previous people left, and when the room is cleaned for the next guest.

In December we stayed at POFQ, arriving to the desk at a little past noon. Our room was ready.

There is a ton of stuff to occupy your time if you need to wait a bit. The resort will store your bags, and you can stroll around. Grab some food at the food court. From your resort you can take the boat to DTD and waste time perusing the shops. Maybe grab yourself a delicious milkshake (it's a must do for me).

Getting a room before 3:00 or 4:00PM depends on any requests you might have. The less requests the better your chances. If you ask for a certain building, certain floor, certain view, connecting rooms, then your chances are less. I've stayed more than 60 times now in the last 15 years and I average about 10% of the times I get in early. The other times I spend the day at the park and check back several times throughout the day. We usually check in about 11:00AM.

I've checked in around 11am 3 times. At POR, we had to wait until 1 to get into our room. At CBR, we had to wait until 3. At CSR, we got right in. But we were able to store our things amd have lunch at the food court while we waited.